Poly(lactic acid) was flame retarded using cellulose-based intumescing flame retardants. Cellulose was an excellent carbon source in combination with ammonium polyphosphate (APP), exhibiting good thermal stabilities and UL-94 ratings of V-0. Nanofibrillated cellulose was phosphorylated to eliminate the need for APP. The fibers were further modified by quaternization and with glycidyl phenyl POSS to increase the char yield. Fibers were analyzed by elemental analysis, potentiometric titration, and thermogravimetric analysis. The composites exhibited good thermal stability, but failed UL-94.